Recently, with the dramatic increasing demand for handheld electronic products such as laptop computers and mobile phones and the growing demand for electric carts, electric wheelchairs, and electric bikes, studies are being intensively made on high performance secondary battery that can be recharged repeatedly. Also, more recently, with the gradual exhaustion of carbon energy and the increasing interest in environment, the global demand for hybrid electric vehicle (HEV) and electric vehicle (EV) is gradually increasing. Accordingly, deeper interest and more intensive studies concentrate on secondary batteries for vehicle as a key component of HEV or EV.
Lithium ion secondary batteries are the most realistic technology for high performance secondary batteries and secondary batteries for vehicle. A lithium ion secondary battery works by repeated intercalation and deintercalation of lithium ions at a negative electrode and a positive electrode. A lithium salt containing electrolyte in which lithium ions move but electrons do not move is present between the electrodes.
Many studies are being made on secondary batteries in aspects of high capacity and high density, but it is also important to improve life and safety. To this end, it is necessary to inhibit a decomposition reaction with an electrolyte solution on the electrode surface, and prevent overcharge/overdischarge.
Particularly, there is a need to prevent the deposition of lithium, so-called lithium-plating (Li-plating), on the negative electrode surface. The reason is that lithium plating not only causes side reactions with an electrolyte solution and changes in kinetic balance of the secondary battery, resulting in degradation of the secondary battery such as capacity loss, but also affects the life of the secondary battery and causes a safety problem with loss of an overcharge control function.
Conventionally, however, it is very difficult to detect lithium plating in secondary batteries in real time. Earlier non-destructive detection of lithium plating on the negative electrode includes discharging at low temperature, heat capacity analysis, and thickness increase analysis. However, they do not involve measuring in an environment in which a secondary battery is used. Therefore, there is a need for real-time detection of lithium plating in an actual use environment of a secondary battery.